Multi-layer systems have been utilized to coat automobiles for a number of years, but the early development of these systems necessarily employed organic solvents. As environmental regulations became more stringent, and the cost or organic solvents rose, organic-borne basecoat systems became less desirable. The recent research emphasis in the area of multi-layer systems, especially basecoat systems has focused on the development of water-borne systems for multi-layer coatings.
The shift from organic solvents to water for dispersing and applying resins in multi-layer systems solved many of the environmental and cost problems associated with the use of organic solvents. Water-borne systems, however, have resulted in other problems.
The application of a multi-layer coating to an automobile body, for example, would be greatly facilitated by a system that provides for quick-drying of solvent during and after the application of a coating. These quick-drying characteristics enhance a broad application window and allow minimal control of relative humidity and temperature in the spray zone, resulting in lower energy costs. By facilitating drying, the time between coatings would be diminished, resulting in greater manufacturing efficiencies and lower energy costs. In addition, there would be no need for a cool-down zone after drying which would further the manufacturing efficiencies. Low boiling organic solvents were originally used in multi-layer coatings to take advantage of their quick-drying features. With the introduction of aqueous based multi-layer systems, the drying of water from a given resin coating after application became a problem. It was desired to produce a basecoat composition that could be dried in a period of time short enough to maintain manufacturing efficiency.
The present invention is directed to polyurethane coatings to be used in formulating basecoat compositions of multi-layer coating systems. The resins of this invention are shown to possess the qualities of being quick-drying during and after application. Furthermore, the resins of this invention also exhibit superior coating characteristics, for example, good metallic effects such as very favorable arrangement, fixation, and flip effect of the metallic pigments in the paint film. When non-metallic pigments are used, the resins of the present invention exhibit excellent decorative effect.
This invention, therefore, relates to the field of polyurethane coatings for use in automobile basecoat/clearcoat systems. In particular, this invention relates to the discovery that incorporating a long-chain carboxylic acid of at least 50% by weight of the carboxylic acid component used to make polyester resins which are further incorporated into polyurethane resins provides basecoat compositions exhibiting low temperature flash characteristics. These low temperature flash characteristics are exhibited even where the basecoats are deposited at 50-90% relative humidity.
The polyurethane resin, produced by the reaction of the above-described polyester resin and a polyisocyanate mixture, although useful as a coating composition for a number of substrates of especially useful as a basecoat for automobiles. Coatings containing polyurethanes synthesized from polyesters with a long chain fatty acid comprising at least about 50% of the acid component in the polyester resin have shown to be particularly useful for water-borne basecoat compositions used in multi-layer systems.
It is an object of this invention to provide polyurethane resins that can be incorporated into basecoat formulations to provide low flash and quick-drying characteristics.
It is an additional object of this invention to provide polyester resins which can provide favorable low flash and quick-drying characteristics to polyurethane resins.
It is a further object of this invention to provide water-borne basecoat compositions having favorable coating and cosmetic characteristics and additionally provide for manufacturing efficiencies which result from the low-flash, quick-drying characteristics.
It is also an object of this invention to provide a method of producing the resins and basecoat compositions described herein.
It is a further object of this invention to provide a method for coating a metallic or plastic substrate utilizing the resins and basecoat formulations of the present invention.
These and other objects of the present invention are furthered by incorporating polyurethane resins into basecoat formulations.